In a tunneling operations, a machine removes material from the face of the tunnel and moves the removed material rearwardly to be transported to the surface for disposal. As the tunneling machine excavates the tunnel, it is necessary to provide a liner for the tunnel behind the machine. Presently, liners are either wood/steel beams supported by steel ribs, commonly called “rib and lagging”, steel panels or concrete panels. The use of a particular liner system is dependent on ground conditions and cost.
Wood/steel beams supported by ribs have the advantages of lower cost than either steel or concrete panels as well as being easier and faster to install. Presently, the steel ribs are provided in three or more sections which, when connected together end to end, provide either a complete circle for the desired tunnel diameter or the desired shape for tunnel dimensions. The ribs generally are made by rolling an I-beam structure along one flange to form a curved cross section that supports the ends of the wood/steel beams which are installed between two adjacent ribs.
Presently the rib ends are generally connected to one another using plates welded onto the ends of the ribs, typically called butt plates. The butt plates are then connected together by bolts. While such an arrangement provides for a secure connection, it does have certain disadvantages. The installation and tightening of the bolts consumes a significant amount of both material expense and time in the operation of installing the tunnel lining. In addition, the butt plates extend into the interior of the tunnel, thus reducing the effective usable diameter of the tunnel.
There thus remains a need for a less expensive, simpler and quicker way of connecting the steel ribs together.